Long haul internet traffic is often carried by optical fibers. Wavelength division multiplexing (WDM) is a technique whereby transmitters encode and transmit different signals onto different wavelengths of light (e.g. different optical channels) that are combined and carried on the same optical fiber. Optical filters at a receiving end of the fiber separate received light into the various component wavelengths that are provided to separate optical detectors that recover the encoded signals.
In conventional WDM systems, the path from a data source to an optical encoder is generally fixed. For example, FIG. 1 shows a conventional WDM data transmission system 10 that receives data from a number of data sources S1, S2, S3 and S4 and transmits the data over a common optical fiber 40. Such data sources are typically
Internet Protocol (IP) routers but could be other sources of internet data. The data streams from one or more of the sources S1-S4 are applied to a fixed optical transponder 20 having digital signal processors 22, 24, 26 and 28 that transmit the data as modulated light beams. The digital signal processors (DSPs) 22-28 operate to transmit the data as an optical signal having a particular wavelength lambda-1, lambda-2, lambda-3 or lambda-4. In addition, the DSPs may select a modulation type (e.g. QPSK, 8QAM, 16QAM etc.) as well as a type of error checking code with which the data are transmitted.
In conventional systems, the mapping of a particular data source to a particular optical encoder is typically fixed when the transponder is set up. In the example shown, data from source S1 are always transmitted via DSP 22 on wavelength lambda-1, while data from source S3 are always transmitted via DSP 26 on wavelength lambda-3. In some instances this may not optimize the capacity of the fiber optic communication link.
There are occasions where some optical channels using a particular wavelength will have one or more differing channel characteristics compared to other optical channels. Such characteristics can include differing bit error rates, signal to noise ratios, fading, dispersion or leakage from the fiber or other factors which affect the speed and/or accuracy of the data transmission for that channel.